Male great white shark – one to avoid on the dinner table as well. Photo: Richard Vevers
Excess eating of shark in fish and chips and other meals is not just bad for the conservation of the species but may also damage human health, a new study shows.
Analysis of the tissue of 30 dusky, sandbar and great white sharks caught by long lines and in shark nets off the NSW coast found high levels of metals including mercury “that may have negative implications for human consumers”, the study published in the Marine Pollution Bulletin found.
According to the Food Standards Australia New Zealand website, fish is an excellent source of protein but the consumption of some species should be limited because of higher levels of mercury. These include limiting consumption of shark (flake), marlin and swordfish to no more than once a fortnight for pregnant women, while the general population should only eat flake and other fish species once per week, according to the FSANZ.
Dusker shark in Sydney Harbour with swimmer. Photo: SIMS
According to the shark study, in the two highest concentrations of mercury found, two 120-gram servings of either dusky or sandbar shark muscle tissue would be enough to exceed FSANZ’s provisional tolerable weekly intake levels for mercury. Some 75 per cent of the dusky sharks and 58 per cent of the sandbar shark samples exceeded the FSANZ’s maximum mercury limit, the report said.
Vic Peddemors, a shark expert with the NSW government and a co-author of the study, said that while chances “are quite remote” that people would become ill, “it’s obviously not good for you to eat too much shark”.
Sharks are so-called apex predators that accumulate the mercury and metalloids such as arsenic naturally from other species they hunt, said Amanda Reichelt-Brushett, an associate professor at the Marine Ecology Research Centre of the Southern Cross University who is another author of the report.
Shark fin soup might have high arsenic levels. Photo: NYT
Shark fins were found to have high concentrations of arsenic, a result with “implications for regular consumers of these products (i.e. shark fin soup)”, the report said.
While more research was needed to identify the toxicity of the type of arsenic found, Dr Reichelt-Brushett said, food preparation was unlikely to lower concentrations: “I don’t think the method of cooking would have a whole lot to do with the total load of the metal.”
Dr Reichelt-Brushett also noted that the sharks tested were from eastern Australia where pollution levels of mercury and other metals were relatively low. A separate study published in 2013 included sharks caught around Buru Island in Indonesia where arsenic and mercury from a nearby gold mine found even higher concentrations of the metals, she said.
Aside from shark meat and fins, consumers should also be wary of excess consumption of products made from shark livers, such as fish oil. The livers can have high concentrations of methyl mercury, the paper noted.
Metals concentration in the sharks varied according to age and gender, with mature males found to have the highest readings.
“The large males of the species are the ones to avoid in terms of accumulation,” Dr Reichelt-Brushett said, adding that females may reduce their levels through giving birth.